added dns.getHostByAddr() -- resolve an external IP address to hostname(s)

lib/dns.js

@@ -93,11 +93,25 @@ exports.resolve = function (domain, type_, callback_) {
 }
 
 
-exports.getHostByName = function (domain, callback) {
-  channel.getHostByName(domain, dns.AF_INET, callback);
+function familyToSym(family) {
+  if (family !== dns.AF_INET && family !== dns.AF_INET6) {
+    family = (family === 6) ? dns.AF_INET6 : dns.AF_INET;
+  }
+  return family;
+}
+
+
+exports.getHostByName = function (domain, family/*=4*/, callback) {
+  if (typeof family === 'function') { callback = family; family = null; }
+  channel.getHostByName(domain, familyToSym(family), callback);
+};
+
+
+exports.getHostByAddr = function (address, family/*=4*/, callback) {
+  if (typeof family === 'function') { callback = family; family = null; }
+  channel.getHostByAddr(address, familyToSym(family), callback);
 };
 
-var net;
 
 // Easy DNS A/AAAA look up
 // lookup(domain, [family,] callback)
@@ -132,7 +146,7 @@ exports.lookup = function (domain, family, callback) {
     } else {
       if (family) {
         // resolve names for explicit address family
-        var af = (family === 4) ? dns.AF_INET : dns.AF_INET6;
+        var af = familyToSym(family);
         channel.getHostByName(domain, af, function (err, domains) {
           if (!err && domains && domains.length) {
             if (family !== dns.isIP(domains[0])) {